When insulated electric power conductors are combined with insulated communication con- .5 ductors within a common sheath, experience in the past, has proven that interference currents are induced in the communication conductors to such an extent that the signals' being transmitted are distorted, if not rendered completely unintelligible. The use of metallic shielding tapes or shielding braids around either the communication conductors or* the power conductors or both has offered very little eiectiveness in reducing these interference currents.

in accordance with the present invention, the difficulty referred to is overcome by positioning the communication conductors in the center of the area ci a cable section and arranging the power conductors symmetrically or concentrically about them.

The invention taires into considerationthe fact that at the geometric center oi the internal section within a concentric conductor, the elective electric field is zero. When this act is taken into consideration, it is apparent that there is a true and novel cooperative relationship between the communication and power conductors, as the satisfactory operation of the communication conductors is dependent upon the symmetrical relation of the power conductors, so as to prevent distortion of voice modulated currents transmitted, by said communication conductors.

The 'power conductors in the cable considered are applicable'to any type oi wiring circuit, e., single phase empoli/phase, and alternating or direct current.

The combined power and communication cable oi my invention has a wide field oi' application. ior submarine, aerial, and buried installations, sinceA ,he possibility of combining two types of cable within a common sheath effects economy in the cost of cable and the space utllized for installation. (For the same quality of service as provided by this invention, it was formerly required to use two separate cables, each having itsI ovm protective covering, which in the cases of installation outlined above involves metallic armoring which is an expensive operation in cable manufacturing.) The installation cost is also less for the single cable.

An example of an installation requiring the use of a cable design as covered by my invention is in a mine shaft Where power and communication circuits must be brought down from the survface of the mine to the various underground 1937, Serial No. 133,373

levels. A cable for this service must be protected with metallic armor against abrasion and impact, and the available space in the mine shaft for cable installation is usually limited. The cable design covered by my invention will provide vention are exemplied in the accompanying Y drawing, in Which- I Fig. 1 is a perspective elevation with portions of the cable broken through different distances to reveal the interior construction; Fig. 2 is a cross-sectional View thereof; Fig. 3 is` a view similar to Fig. 1, illustrating a modification;

fr is a cross-section thereof; Fig. 5 is an elevation partly broken away to illustrate a further elevation; Mg. 6 is a cross-section thereof; Figs. 7 and 8 are cross-sectional views of further modications.

Referring in detail to the drawing, il@ and lf3' illustrated one pair `of communication conductors, such as telephone wires adapted to transmit voice and 'modulated currents. it and il' represent ancther pair of similar communication conductors. llihes-e are individually provided with any suitable form oiinsulation commonly used in the art and are surrounded, as shown, by a wrapping or binder t2 and insulation Cabled concentrically about the body of insulation H3, there is a power transmission conductor ll. The strands composing this conductor, as clearly shown in Fig. 2, are arranged concentrically about the central longitudinal axis oi the cable as a Whole and the communication conductors are also arranged concentrically v about said axis. Surrounding the power cable tl, there is a body of insulation i5. Outside of this, there is a plurality of circularly arranged strands, which comprise another power cable it.

These strands, as clearly shown in Fig. 2, are

circularly arranged and are concentric with the longitudinal axis of the cable. @utside of the cable I6, there is a body of insulation ii, as described hereinbefore and an outer protective sheath I8, which may consist of metallic armoring or any other type of protective covering known in the art.

'1n the modification of Fig. 3, the communication conductors are substantially the same as in Fig, 1 and they are correspondinglynumbered.

They are similarly covered with a wrapping or binder I2 and a layer of insulation it. In this modification, one of the power cables is in the form of a ribbon-like strip, indicated at id'. This is surrounded by a body of insulation H5' over which there is laid another power conductor in the form of a similar ribbon-like strip, indi cated at I6. Outside'of the strip it, there is a body of insulation lll' and an outer protective sheath l 8'; As clearly shown in Fig. 4, the power cables I4 and iti are arranged concentrically about the axis of the inner group of .communication conductors.

In the modification of Figs. 5 and 6, I have shown a multiplicity ci communication con1 ductors located centrally of the cable as a whole. These are indicated generally by reference character Ill-l i. ductors are symmetrically arranged about the central longitudinal axis o the cable. They are surrounded by a wrapping or binder t2". Arranged symmetrically about the communication cables, there are a plurality of power conductors, indicated at E9, 2D, 2i and 2i?. Each of these conductors is surrounded with a body of insulation I9', 20', 2l', 22', as shown and between the insulated power cables there is suitable filling material indicated at 23. Surrounding conductors i9, 2t), 2i and 22 and ller 23, there is a wrapping or binder il and an outer protective sheath i8'.

. In the modication of Fig. 7, I have shown a central group of communication conductors it" and il. Arranged symmetrically about' this group of conductors are three power conductor cable units 24, 25 and 26, each unit being of the sector type and being surrounded with theV conventional form of insulation, the entire assemblage being enclosed in a wrapping or binder il!" and an outer protective sheath iti.

In the modification of Fig. 8, the central group of communication conductors iii, it', ill and tt are symmetrically grouped about the central longitudinal axis of a cable which is of substantially elliptical shape in cross-section. -In this modication, there is an inner power transmission cable comprised of a plurality of elliptically arranged strands 28, which are symmetrically arranged about the central longitudinal axis of the cable as a whole.` Spaced away from the power cable 28 by a suitable body oi insulation, there is another power cable 29, the individual conductors or strands of which are also symmetrically arranged about the central longitudinal axis of the cable as a whole. There is a body of insulation 30 surrounding the outer power cable 29 and the entire assemblage is enclosed in an elliptical protective sheath 3i,

In all of the cases illustrated, the communication conductors may be twisted together and enclosed within one or more conductors adapted to carry power transmission currents, the power conductors being in the form of a plurality of concentric strands of copper, or other` suitable conducting material arranged symmetrically about the center of the-inner group of communication This group of communication conamarsi conductors. By such a symmetrical or concentric arrangement of the respective communication and power conductors, the voice modulated cui'- rents transmitted by said communication conductors will not be distorted by the power currents transmitted by the power conductors.

Various modifications may be made by those skilled in the art without departure :from the invention as defined in the appended claims.

What I claim is:

l. A modulated communication circuit land a power transmititng circuit comprising a cable having an inner group of insulated conductors for transmitting modulated currents of said communication circuit and an electric power transmission circuit comprising a plurality of outer power current conductors to conduct alternating currents of said power transmitting circuit and arranged symmetrically about said inner group of conductors to provide a zero electric iield at said inner group of conductors and to prevent distortion of the currents transmitted by said inner group of conductors.

2. A modulated communication circuit and a power transmitting circuit comprising a cable having an inner group of insulated conductors transmitting modulated communication currents of said communications circuit and arranged symmetrically in pairs about a central longitudinal axis and a plurality of electric power conductors to conduct alternating currents of said power transmitting circuit and arranged concentrically about said axis and with intervening insulation between said power conductors and saidinner group of conductors, said electric power conductors being arranged to provide a zero electric iield in the area of said inner modulated communication conductors and to prevent distortion of the currents transmitted by said inner group of conductors.

3. A telephone circuit and a power circuit comprising a cable having an inner group of individually insulated conductors transmitting Voice modulated currents of said telephone circuit and an electric power transmission circuit comprising a plurality of power conductors to conduct alternating currents of said power circuits insulated from one another and arranged concentrically and symmetrically about 'the inner group of conductors of said telephone circuit to provide a zero electric field within said inner group of telephone conductors.

4. A telephone circuit and a power circuit comprising a cable having an inner group of individually insulated telephone circuit conductors to transmit voice modulated currents, a circular body of insulation surrounding the latter and a plurality of circularly arranged power conductors to conduct alternating electric power currents, said conductors being coaxially posi- 'ing the power conductors .from one another.